1. Field of the Invention
The present invention relates to a memory, and more particularly, it relates to a memory refreshing data stored in memory cells.
2. Description of the Background Art
In general, a DRAM (dynamic random access memory) is known as an exemplary memory refreshing data stored in memory cells, as disclosed in Japanese Patent Laying-Open No. 2001-229674, for example. The conventional DRAM disclosed in Japanese Patent Laying-Open No. 2001-229674 performs a normal access operation (read or write operation) synchronously with a first clock signal having a prescribed cycle and performs a refresh operation synchronously with a high-speed second clock signal having a cycle shorter than the prescribed cycle of the first clock signal, thereby performing the refresh operation in an idle time between normal access operations. On the other hand, a ferroelectric memory utilizing pseudo capacitance change responsive to the polarization direction of a ferroelectric substance as a memory element has recently been known as another exemplary memory refreshing data stored in memory cells. In relation to this ferroelectric memory, disturbance is known as a phenomenon causing data disappearance in a rewrite operation following a read operation or a write operation on memory cells including ferroelectric capacitors due to reduction of polarization quantities of the ferroelectric capacitors caused by application of a prescribed voltage to memory cells connected to word lines other than a selected word line. In order to suppress this disturbance, the conventional ferroelectric memory refreshes the data stored in the memory cells.
In the aforementioned DRAM disclosed in Japanese Patent Laying-Open No. 2001-229674, however, current consumption is disadvantageously increased due to the refresh operation with the high-speed second clock signal having the cycle shorter than that of the first clock signal employed for the normal access operation. Also when the technique related to the refresh operation of the DRAM disclosed in Japanese Patent Laying-Open No. 2001-229674 is applied to the refresh operation of the ferroelectric memory, current consumption is still disadvantageously increased.